<x-flowed><< Clean the carbon around the SP holes. Are there any cracks leading out to the
valve seats?

This is a 72-3 left side FI head. The threaded boss is for the cyl head temp
sensor and the hole is for a breather tube. This head originally had a step in
the combustion chamber that the cylinder sealed against, to reduce the
compression ratio. Is that step still there?

That's a poor head for your engine, mainly because of the breather hole, which
explains all the oil around that side. If the step is still there, I'd very
much like that head since they are very hard to find in unmolested condition. I
have good, OE heads that I could swap you for it that would be better for you
and your engine. <<

I posted pictures of the crack between the SP and the intake valve.
It's small, but there.

I also posted pictures of what appears to be a step in the cylinder
sealing surface. No indication of compression deforming the material.

For those interested but not quite visualizing the boss and vent
Jim mentions, I've posted an overview of the head showing them.

I tore enough of the engine down (in the car still, such a masochist!)
to find that the left head matches the right. I assume the step would
be the same. I haven't removed the left head yet.